Python Strings

What is Data Type?

It is an attribute that tells what kind of data that value or a variable can have it.

#Example:
rollnumber  = 12345 # rollnumber  is integer
name = "Anand" # name is string
marks = 80.5  # marks is float

Standard Data Types

  1. Numbers
  2. Strings
  3. List
  4. Tuple
  5. Dictionary

Python Strings

  • A string is a sequence of characters.
  • It is represented by either single quotation marks, or double quotation marks.
  • Even triple quotes can be used in Python but generally used to represent multiline strings and docstrings.
  • Note: Python doesn’t have any separate data type for characters so they are represented as a single character string

    How to create a python string?

    #Sample Code
    singlequote = 'Python String'
    print(singlequote)
    
    doublequote = "Python Tutorials"
    print(doublequote)
    
    # triple quotes string can extend multiple lines
    triplequote = """Welcome to Vinoth Rathinam
                        Tutorials"""
    print(triplequote)
    
    Output:
    Python String
    Python Tutorials
    Welcome to Vinoth Rathinam
                        Tutorials
    

    Accessing Values in Strings (Slicing)

  • We can access individual characters using indexing and a range of characters using slicing.
  • Index starts from 0.
  • Left to right direction
  • #Sample Code
    myString = "Python for Machine Learning"
    
    #print first Character
    print(myString[0])
    
    #slicing 11th to 18th characters
    print(myString[11:18])
    
    # Using the defalut values - Use it as per the requirement
    print(myString[:])
    print(myString[11:]) 
    print(myString[:11])
    
    Output:
    P
    Machine
    Python for Machine Learning
    Machine Learning
    Python for 
    

    Negative Indexing

  • Python allows negative indexing for its sequences.
  • Index starts from -1
  • Right to left direction
  • The index of -1 refers to the last item, -2 to the second last item and so on
  • # Sample code to slice the strings
    myString2 = "Python for Automation"
    
    #print last character using negative indexing
    print(myString2[-1])
    
    print(myString2[-2])
    
    print(myString2[-5])
    
    #slicing 7th to 2nd last character
    print(myString2[7:-2])
    
    Output:
    n
    o
    a
    for Automati
    

    Index out of the range

  • If we try to access index out of the range or use decimal number, we will get "IndexError"
  • The index must be an integer. We can't use float or other types, this will result into TypeError.
  • Python allows negative indexing for its sequences
  • # Sample code for IndexError
    myString3 = "Python"
    print(myString3[6])
    
    Output:
    ---------------------------------------------------------------------------
    IndexError                                Traceback (most recent call last)
    <ipython-input-25-4f411a63679a> in <module>()
          1 # Sample code for IndexError
          2 myString3 = "Python"
    ----> 3 print(myString3[6])
    
    IndexError: string index out of range
    
    # Sample code for TypeError
    print(myString2[1.5])
    
    Output:
    ---------------------------------------------------------------------------
    TypeError                                 Traceback (most recent call last)
    <ipython-input-26-3f161d7da838> in <module>()
          1 # Sample code for TypeError
    ----> 2 print(myString2[1.5])
    
    TypeError: string indices must be integers
    

    How to change or update a string ?

  • Strings are immutable. This means that elements of a string cannot be changed once it has been assigned.
  • We can simply reassign different strings to the same name.
  • # Creating a string and checking the memory address
    str1 = "Python "
    print(str1)
    print("Memory location before update",id(str1))
    
    # Trying to modify the string
    str1 += "Tutorials"  # str1 = str1 + "Tutorials"
    print(str1)
    print("Memory location after update",id(str1))
    
    Output:
    Python 
    Memory location before update 1825268075800
    Python Tutorials
    Memory location after update 1825268818328
    
    # Updating the String Value
    myStr = "Happy Learning"
    print(myStr)
    myStr[4] = 's'
    
    Output:
    Happy Learning
    ---------------------------------------------------------------------------
    TypeError                                 Traceback (most recent call last)
    <ipython-input-29-85c0b5e71d2c> in <module>()
          2 myStr = "Happy Learning"
          3 print(myStr)
    ----> 4 myStr[4] = 's'
    
    TypeError: 'str' object does not support item assignment
    

    How to Delete a String?

  • We cannot delete or remove characters from a string.
  • We can delete the string entirely using the keyword "del"
  • # Code to delete complete string
    del myStr
    print(myStr)
    
    Output:
    ---------------------------------------------------------------------------
    NameError                                 Traceback (most recent call last)
    <ipython-input-31-ede3757523fc> in <module>()
    ----> 1 print(myStr)
    
    NameError: name 'myStr' is not defined
    
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